New ICF Constructed Home
A year-round creek in the backyard, a large adjacent greenbelt and abundant sunshine were major appeals. This down-sloping lot was considered unbuildable by local contractors because of the narrow building envelope between the front and rear set backs required by the creek floodplain. But for a professional mountain climber, one man’s “unbuildable” is another man’s playground.
This home was built with contemporary levels of comfort and style that saves energy without calling attention to itself; where the energy efficiency of this home was built-in, not added on.
Building Construction Type:
The designers/builders chose insulated concrete forms (ICF) for their combination of structural strength, longevity, energy efficiency and soundproof performance. The home was sided with stucco on the first floor and fiber- cement on the upper floor. The fiber-cement has a fifty-year warranty, while the baked-on redwood finish is warranted for 12 years. Given the cost of re-staining wood siding every two years, this made the siding cheaper than free…and it’s fireproof. More importantly, they also saved the environmental costs of aerosol paint spray, especially in proximity to the creek.
The steep down slope design required retaining walls on the street side of the home. With ICF, this was no more complicated than building any of the other walls, with the exception of the extra layer of waterproofing along the earth-contact surfaces.
Site Use & Protection (LEED Cat. I):
Silt-fencing was immediately set along the floodplain setback to prevent any construction dirt or debris from reaching the watershed. Upon completion of the framing, it was terraced with dry-stacked rock to stabilize the slope and encourage native vegetation.
In Planning Energy Efficiency & Renewable Energy Measures Used in project (LEED Cat. III):
The walls are Insulated Concrete Forms (ICFs) with an insulation value of approximately R-50. The roof is insulated with soy-foam over the living areas and blown-in cellulose over the garage. Energy Star appliances were utilized through out the home, as well as low-E double-pane windows.
The owners chose a high-efficiency forced air gas heating system for three reasons. 1) The energy efficient construction of the house requires minimal auxiliary heating and no cooling at all beyond opening a few windows. 2) Forced air gives you heat in seconds, not hours. 3) Forced-air heating costs less than half as much to install as hydronics.
They used dual-pane, low-E glass with primary glazing to the east both to take advantage of the creek, forest and mountain views, but also to maximize morning warming, the most important heating time for the house. With its enormous thermal mass and miniscule thermal losses to air movement, this ICF house holds most of the heat it absorbs and produces.
Materials & Resources (LEED Cat. IV):
Trex Brasilia was used for the decking. It has a substantial recycled component, low maintenance, and is resistant to fungus. The carpet is polyester from recycled soda bottles. It has a plush feel and is soft to the touch, similar to fleece.
Interior Environmental Considerations (LEED Cat. V):
Low- and no-VOC water-based paints, stains and varnishes were used throughout the house. Planned use of air/air heat exchanger.
Can a house be too soundproof? With heavily insulated floors and soundproof interior walls this house sounds like it’s miles from the nearest road, not forty feet from the second busiest street in Tahoe Donner. The only drawback is that calling the kids to dinner means walking downstairs or using an intercom.
Beyond annual savings on heating and cooling bills, well-planned green building needs to factor in full life-cycle costs. If a well-built wood house lasts 150 years, we have to assume it must be torn down and replaced every six generations or so. Since concrete Roman aqueducts still carry water to Rome 2000 years after construction, we might safely assume an ICF house will last from two to ten times longer than a wood house. How many trees, how many man-hours, and how many trips to the lumber yard and hardware store does that represent in energy savings? A lot. Factor in heating and cooling savings over that extended multi-generational lifetime, and it makes a pretty persuasive case for ICF construction. Besides, the house literally feels as solid as a rock. No wood house feels as quiet, stable or protective.
Subjective Evaluation/ Design Considerations: How well has the structure achieved its design goals? What would be done differently the next time?
The owner/builders said they would add an intercom system, and because the house is so airtight, they would also install an air-to-air exchanger prior to finishing the garage. Air movement in the winter without opening the windows can be limited.
Contrary to ICF manufacturer’s hype, they also said they would hire at least one project supervisor with experience in ICF construction. They found that “doing it yourself easily” with “no experience necessary” was far from the reality.